S4 MORPHOLOGY AND EVOLUTION Classification.—There is now a consensus of opinion that there is only one species of Orang, but there are local varieties. There is, however, considerable doubt as to the exact number of varieties. Various zoologists have made use of the characters of the skull and teeth, the colour of the hair, the presence or absence of cheek-pads and of nails on the great toe for purposes of classification ; but all these characters vary with age and sex. The skull never attains a fixed form, but it changes throughout the whole life period; and a series of photographs of the same animal from youth to old age would exhibit striking differences. Besides these osseous differences there are variations in the bulk of the muscles of mastication, which produce differences in the contour of the head. So it is evident that one cannot give any clear description of the actual local varieties, either in number or in characters ; Briihl (235) and Dumortier (245, 246) have described the changes in the head and the characters of species. Selenka (287) described six varieties in Borneo and two in Sumatra. Giglioli (447) considered that there are two species in Borneo, and Pitzinger (248) believed there are four species.* It is now believed that Owen's Lesser Orang (Simia morio) was not a distinct species, but merely a young Simla satyrus. * Abel (224), Hartmann (452), Hornaday (256), Mohnike (371), Mtiller (87), Bosenburg (279A), Schlegel and MtUler (282), Selenka (287), Trinchese (292), Veth (292A), Wallace (293), Wenckstern 297), and others have recorded localities in which specimens were observed or shot.